hydrat

Hydrat is a term used in chemistry and mineralogy to refer to a compound that contains water molecules as an integral part of its crystal structure. The water is known as water of crystallization and is bound to the substance in a fixed ratio. Hydrates are commonly written with a formula that includes the number of water molecules, for example copper sulfate pentahydrate CuSO4·5H2O or calcium sulfate dihydrate CaSO4·2H2O (gypsum).

Hydrates form by crystallization from an aqueous solution or by chemical hydration of an anhydrous salt. The number of water molecules in a hydrate depends on the substance and conditions such as temperature and humidity. Hydrates can often be dehydrated by heating or chemical treatment, producing the anhydrous form; in many cases the process is reversible, with the ability to reabsorb water from the surroundings.

There are different classes of hydrates. Inorganic hydrates include salts with water of crystallization. Clathrate hydrates, or gas hydrates, consist of a lattice of water molecules that traps gas molecules such as methane or carbon dioxide under high pressure and low temperature. These hydrates are of interest in energy resources, climate science, and planetary geology.

Applications of hydrates include moisture control, drying agents, and roles in materials science. Gypsum is a widely used hydrated mineral in construction; copper sulfate pentahydrate serves as a laboratory reagent and in mineral identification. In pharmaceuticals, some drug substances are isolated or stored as hydrates, affecting stability and solubility. The study of hydrates links water chemistry with solid-state structure and phase behavior.